Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

cyberus-technology.de

Post reply on HN
Print view View original

111–120 of 337 posts

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#111

Post by chx »

strmpnk wrote: post #108
INTPenis wrote: post #104

So I'd love to post an Ask HN: Which AMD Laptops would you recommend for work, alternatives to Thinkpads? I've noticed some Thinkpads with AMD CPUs but I feel like I'm on virgin ground when it comes to AMD and their integrated GPU offerings.

I've been eyeing more release details on the ThinkPad X395 which was recently announced. "Coming Soon" is probably means early June for some select configurations. I think these will fit in the premium/professional laptop space better than some of the bargain laptops that carried AMD chips in the past. I believe others OEMs are developing similar offerings as well but I can't find any quick links for newer SKUs like…

Yes the T495 and the X395 ought to be the best ones.

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#112

Post by als0 »

daeken wrote: post #12
penagwin wrote: post #8

Earlier quoted context omitted.

Not arguing just asking, but how has Pandora's box been opened with the discloser of Spectre and Meltdown? We've had security researchers discovering and reporting vulnerabilities since there were computers as far as I know? I do agree that this won't end soon though. It appears to me that many of the methods CPU's use for better performance are fundamentally flawed in their security, and it's not like we can expect…

Before Spectre and Meltdown were disclosed publicly, very very few security researchers were looking at the CPU level, beyond things like attacks against hardware virtualization functionality, TrustZone and friends, ME, etc. Those bugs had existed for ages and could've been found through thorough examination of the processor manuals, but nobody had really looked too hard there. These new bugs were found independently…

> and could've been found through thorough examination of the processor manuals, but nobody had really looked too hard there.

I don't think you're giving enough credit. The actual microarchitecture isn't documented much in those manuals, so looking hard at those wouldn't help without making a series of assumptions of how it all works. The authors of recent exploits have been diligently reverse engineering and making sensible guesses.

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#113

Post by gmueckl »

ccozan wrote: post #102
School-Cotton wrote: post #81

Earlier quoted context omitted.

To give ballpark numbers: modern Intel processors can retire a few instructions per cycle in tight loops (4 is the theoretical maximum; > 2 is realistic in a lot of high-performance code). A branch misprediction wastes 10-15 cycles. So getting rid of speculation entirely, and stalling on every branch, would waste time equivalent to dozens of instructions. On typical code that has a branch every few instructions, this…

Can we actually compute without branching? Genuine question. What architecture would do that, and how?

The simplified SIMD cores in early GPUs had to fake branching to some extent for their virtual threads: every branch in the shader code would be tested for each virtual flag and that thread (really just a vector component) would be masked out for the instructions of the branch that didn't apply. The GPU would run both branches, relying on the mask. It was workable, but very slow.

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#114

Post by fakwandi_priv »

Apparently Intel attempted to play down the issue by trying to award the researchers with the 40,000 dollar tier reward and a separate 80,000 dollar reward as a "gift" (which the researchers kindly denied) instead of the maximum 100,000 reward for finding a critical vulnerability.

Intel was also planning to wait for at least another 6 months before bringing this to light if it wasn't for the researchers threatening to release the details in May.

Source in the dutch interview: https://www.nrc.nl/nieuws/2019/05/14/hackers-mikken-op-het-i...

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#115

Post by derefr »

founderling wrote: post #100
IgorPartola wrote: post #84

So at what point do we start producing CPUs specifically aimed at running a kernel/userland? Why don't we have a CPU architecture where a master core is dedicated to running the kernel and a bunch of other cores run userland programs? I am genuinely curious. I understand that x86 is now the dominant platform in cloud computing. But it's not like virtualization needs to be infinitely nested, right? Why not have the ho…

You cannot give each VM their own core. The business model of the cloud is that multiple VMs with virtual cores run on a single real core.

At the low end, sure. At the medium-to-high end, each VM is bound to one or more physical cores of the host, or sometimes an entire host ("dedicated instances.")

I don't know enough about the IaaS market to know what the relative revenues of low-end compute vs. medium-to-high-end compute are for your average vendor, though. Is most of the profit in the low end?

I'm also curious on what the impact on margins would be if IaaS vendors decided to switch away from serving the low-end compute demand with "a few expensive high-power Intel cores per board, each multitasking many vCPUs", to serving the demand with "tons of cheap low-power ARM cores per board (per die?) with each core bound to one vCPU."

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#116

Post by Shelnutt2 »

INTPenis wrote: post #104

So I'd love to post an Ask HN: Which AMD Laptops would you recommend for work, alternatives to Thinkpads? I've noticed some Thinkpads with AMD CPUs but I feel like I'm on virgin ground when it comes to AMD and their integrated GPU offerings.

If you don't need a dedicated GPU, the APU offers from AMD are great. They have native linux drivers for everything (on the AMD side, double check the nic/touchscreen/touchpad). I'm using an HP envy x360 15z with a AMD Ryzen 2700u running gentoo and love it. The HP envy has a weird keyboard, but it was a good tradeoff for the AMD setup when I bought it last year.

There is a much larger market in 2019 for AMD laptops, so you should be able to find something to suite your needs.

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#117

Post by deathanatos »

pcwalton wrote: post #73
faissaloo wrote: post #18

Earlier quoted context omitted.

I wonder at what point the hardware fix for these issues stop becoming worthwhile and if we'll see a resurgence of processors without speculative execution or any of these other speed ups.

You can kiss any semblance of reasonable performance goodbye if you eliminate "speculative execution". Pipelining is the most basic tool in the toolbox. Even microcontrollers do it.

Pipelining isn't strictly the same thing as speculation, though, is it? If I have,

  add %rax, %rbx
  add %rcx, %rdx
I can pipeline those without needing to speculate on anything. If there is a dependency on a previous instruction, then we might have to speculate, but hopefully there is still some case for pipelining?

Have any of these bugs been completely based on speculation, or is it always speculating across privilege boundaries? (Although I feel like even the former isn't same, e.g., if you're in some form of VM attempting to maintain privilege separations.)

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#118

Post by easytiger »

fakwandi_priv wrote: post #114

Apparently Intel attempted to play down the issue by trying to award the researchers with the 40,000 dollar tier reward and a separate 80,000 dollar reward as a "gift" (which the researchers kindly denied) instead of the maximum 100,000 reward for finding a critical vulnerability. Intel was also planning to wait for at least another 6 months before bringing this to light if it wasn't for the researchers threatening t…

You have to admire the complex complicity. Someone smart enough to understand the depths of the problem had to guide that conversation

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#119

Post by dragontamer »

IgorPartola wrote: post #84

So at what point do we start producing CPUs specifically aimed at running a kernel/userland? Why don't we have a CPU architecture where a master core is dedicated to running the kernel and a bunch of other cores run userland programs? I am genuinely curious. I understand that x86 is now the dominant platform in cloud computing. But it's not like virtualization needs to be infinitely nested, right? Why not have the ho…

> Why don't we have a CPU architecture where a master core is dedicated to running the kernel and a bunch of other cores run userland programs?

How will your "userland core" switch to other userland programs safely? A pointer-dereference can be a MMap'd file, so its actually I/O. This will cause the userland program to enter kernel-mode to interact with the hardware (yes, on code as simple as blah = (this->next)... the -> is a pointer dereference potentially in a mmap'd space to a file).

So right there, you need to switch to kernel mode to complete the file-read (across pointer-dereference). So what, you have a semaphore and linearize it to the kernel?

So now you only have one-core doing all system level functions? That's grossly inefficient. Etc. etc. I don't think your design could work.

Re: ZombieLoad: Cross Privilege-Boundary Data Leakage on Intel CPUs

#120

Post by ynnn »

yalok wrote: post #106

> macOS performance: Testing conducted by Apple in May 2019 showed as much as a 40% reduction in performance with tests that include multithreaded workloads and public benchmarks. Performance tests are conducted using specific Mac computers. Actual results will vary based on model, configuration, usage, and other factors. from here: https://support.apple.com/en-us/HT210107

Yeah, if you choose to turn off hyperthreading. Pretty expected tbh - hyperthreading helps quite a bit for some things.
Post reply on HN